Microwave switch having diodes situated in the waveguide channels to control coupling between common and branch channels



April 3, 1965 J. v. SMITH ETAL 3,178,659

MICROWAVE SWITCH HAVING DIODES SITUATED IN THE WAVEGUIDE CHANNELS TO CONTROL COUPLING BETWEEN COMMON AND BRANCH CHANNELS Filed March 8, 1962 3 Sheets-Sheet 1 JOHN V. SMITH GEORGE W. LUKE Jr. mvENTbRs BY z 2:

ATTORNEY w 2 2 0 6 m 8 h 1 7% u 1 m s 0 a 2w G a a 7 a x E e I 2 I 9 H M h 0 2 w m s m 0 g E o s ii a H C I I 3 T k Q 0 I W a 0 7' D T 3 2 E E m A B E H m m a w i M m M ..:,....:55255557 6 v HS w c 0 8 B l T E O H m 3 m [D C C I 0 Q i 2% M 7 0 V m M M 2 2 O m w.,:i5:555:55:i M O 3 5 H T 3 0 S a Q 5 n H m 2 a 0 3 x d 7 M I E 2 5 w w w M m u u v 1H 3 m M 11 1 M 8 a M 0 w a 7 a M .n 2 I 9 7 2 3, m M 1 a I 1 M G 7 z 1 A A 2/; me v I H ./.v a TM 1 A n F 2 JOHN v. SMITH GEORGE w. LUKE Jr.

mvENrbRs FIG. 3.

ATTORNEY Apnl 13, 1965 J. v. SMITH ETAL 3,178,659

MICROWAVE SWITCH HAVING DIODES SITUATED IN THE WAVEGUIDE CHANNELS TO CONTROL COUPLING BETWEEN COMMON AND BRANCH CHANNELS Filed March 8, 1962 3 Sheets-Sheet 3 Ill GEORGE W. LUKE Jr.

INVENTDRS BY MW ATTORNEY United States Patent 3,178,659 MICROWAVE SWITCH HAVING DIODES SITU- ATED IN THE WAVEGUIDE CHANNELS T0 CONTROL CUUPIJING BETWEEN CGMMON AND BRANCH CHANNELS John V. Smith and George W. Luke, Ira, Silver Spring,

Md., assignors to the United States of America as representedby the Secretary of the Navy Filed Mar. 8, 1962, Ser. No. 178,514 7 Claims. (Cl. 3337) This invention relates in general to microwave switches and more particularly to high speed multiple throw waveguide switches.

Many microwave systems require high speed multiple channel switching with low insertion loss and good isolation. Prior art switches of this type are of the mechanical variety and as such are of limited speed and are usually quite ineflficient. These prior art multiple channel switches depend for operation on the alignment of a waveguide section located on a central rotor with a particular waveguide section on the stator. Alignment is achieved through mechanical rotation of the central rotor. Due to the use of moving parts and because of the necessary critical alignment of the moving parts, construction of these switches is difficult and expensive and results in a structure which is highly susceptible to breakdown.

The present invention provides for completely electrical switching of microwave energy and is based on the use of semi-conductor diodes in waveguides to perform the switching action. Some semi-conductor diodes exhibit large RF impedance changes under varying bias conditions and therefore are potential switching elements for microwave power. A change of bias can change the input impedance of a waveguide with a diode from an approximately matched to a strongly mis-matched case which results in pass and no pass conditions. Applications of this principle according to the invention provide several switching configurations all exhibiting the proper-- ties of high switching speed and efiicient operation.

An object of the present invention is the provision of an improved high speed waveguide switch.

Another object of the invention is the provision of a. high speed waveguide switch which is entirely electrical in operation.

Still another object of the invention is the provision of a multi-channel waveguide switch having low insertion loss, high speed and good isolation.

A further object of the invention is the provision of a. high speed multi-channel waveguide switch capable of handling relatively high power.

Still a further object of the invention is the provision of a high speed waveguide switch which has wide-band characterstics.

Other objects and many of the attendant benefits of this invention will be readily appreciated as the same be-' comes better understood by reference to the following:

detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 is a perspective of an eight throw microwave switch forming one embodiment of the invention;

FIG. 2 is a cross-section of the microwave svwitch taken along line 22 of FIG. 3;

FIG. 3 is a transverse section of the microwave switch taken generally along line 3--3 of FIG. 1;

FIG. 4 is a schematic diagram illustrating microwave switching using two crystals;

FIG. 5 is a top plan View of a Y-shaped switch forming a second embodiment of the invention; and

FIG. 6 is a cross-section taken along line 6-6 of FIG. 5.

A single pole eight throw switch forming one embodi- 3,178,659 Patented Apr. 13, 1965 ment of the invention is shown in FIGS. 1 and 2. Like numbers have been used to designate like parts wherever possible throughout the views. The body of the switch is circular in shape and consists of a pair of upper and lower mounting plates 10 and 11 having a plurality of waveguides 12 sandwiched therebetween. The upper mounting plate It) carries a number of input connectors 13 which extend into each of the waveguides 12 at their outer ends. I

A central cavity 15 is formed by the intersection of adjacent waveguide walls. An output probe 16 is mounted in the center of cavity 15 in such a manner as to receive energy emanating from any or all of the waveguides 12. The upper mounting plate 10 has a centrally located flange 18 for accommodating a tuning plug 19 which may extend into the central cavity 15 and is designed to provide a limited range of tuning to the switch. At the periphery of the central cavity 15 across the narrow dimension of each waveguide 12 is mounted a diode crystal 20 carried by an RF choke crystal mount 21. The crystal 21B is positioned to control the transmission of energy from the waveguides 12 to the central cavity 15.

Looking more closely to the structural details of the switch shown in FIG. 3, the input connector 13 is of standard configuration, consisting of an outer body shell 25, which is soldered to the upper mounting plate 10 at 26, and a center probe 27 separated from the shell 25 by suitable insulation 28. The center probe 27 is stepped for 'broadbanding and is enclosed in a dielectric sleeve 29 which provides the standard 50 ohm input impedance. These coaxial input connectors are matched to the waveguides 12 in the well-known manner by positioning them a quarter wavelength from the end wall thereof.

Each crystal iii is supported in an RF choke type crystal mount 21 which consists of lower housing 31 insulating spacer 31, crystal holder 32, choke 33, crystal anchor 34, insulating spacer 35 and ground cap 36. The choke 33 contains an annular groove 37 whose depth is such as to provide a short circuit to any energy entering it from waveguide 12. For this reason there are no reflected waves oil of crystal Ell in the waveguide 12. The crystal 26 is surrounded by a dielectric sleeve 33 which is designed to alter the field pattern in the guide 12 so as to match the crystal to the guide and to increase the elficiency and power handling ability of the crystal 20. The crystal holder 32 carries an input contact 3% which is designed for contact with the standard coaxial connector.

The central cavity 15 of the switch is dimensioned for desired physical size and optimum voltage standing wave ratio. It has been found that an optimum standing wave ratio is obtainable for several cavity diameters. The particular one of these optimum diameters chosen will thus depend on such things as overall switch size, number of inputs required, and frequency range to be employed.

The output probe 16 extends into the cavity 15 and forms a part of output assembly at which consists of outer housing 41, inner conductor 42 and insulating spacers 43. The inner conductor 42 is stepped along its length to maintain the ohms impedance characteristic of the standard output connector. In addition the length of inner conductor 42 between the insulating spacers 43 is designed to equal an odd number of quarter wavelengths so as to prevent impedance discontinuities between the spacers 43 and the dielectric of the air space 44. The overall length of the output assembly is a matter of choice determined primarily by the physical orientation of the switch in the system in which it is being utilized.

A tuning plug 19 is threadedly engaged in a flange 18 in upper mounting plate It and provides the switch with approximately a 1000 mc. tuning range. The plug 19 contains a central bore 519 for accommodating output probe 16 which extends through the central cavity 15 and into the aperture formed by flange 1% The output probe 16 was designed to extend into tuning plug 19 so as to broaden the band of the central cavity 15. It the probe 16 were to terminate adjacent the tuning plug, the field from the probe 16 to the plug 19 would have a cosine distribution and would be very narrow band. By allowing the probe 16 to extend into the tuning plug 1 the field distribution from the probe to the plug will be linear and broad band. With this configuration tuning is accomplished by varying the volume of the cavity 15 and also by varying the electrical length of the output probe 16, both of which result from axial movement of tuning plug 19. The flange 18 carries a pair of set screws 51 for locking the plug 19 in place thereby preventing movement of the plug after the switch has been tuned. The screws 51 are preferably made of plastic material to prevent damage to the threads on plug 1% when the screws are tightened.

In operation of the single pole eight throw microwave switch described in conjunction with FIGS. 1, 2 and 3, the switch must first be tuned to the proper frequency required by its intended use. The switch is tuned with a bias voltage applied to but one of the crystals 29 so that it is effectively transparent in the waveguide 12. Energy of the proper frequency is introduced into the switch via the associated input connector 13 and tuning plug 19 is adjusted until a maximum voltage is detected at the output 41?.

During operation of the switch, energy applied to input connectors 13 is radiated down the waveguide 12 by the input probe 27 which is positioned to be properly matched to the waveguide. This energy passes down the guide to the crystal 20 located at the edge of the central cavity 15. The Philco IN263 crystal has been used in conjunction with the embodiment described. However, it is to be understood that other types of crystals may be used with varying success. As shown in FIG. 3, the crystal 20 is connected through crystal anchor 34 to the upper wall of the waveguide 12. With no voltage applied at the input 3? of the crystal mount 21, the crystal 20 will present a high reactance directly across the waveguide thereby reflecting with high frequency any energy radiated down the waveguide 12. With no bias applied to any of the crystals 29 little or no output will be detected at the switch output iii.

It now a voltage bias is applied to one of the crystals 20, this crystal will present a reactance across the waveguide 12 such that energy will be radiated down the waveguide. This energy will then reach the central cavity 15 and will be picked up by output probe 16. In this manner energy may be switched from any of eight inputs 13 to the single output 49 in an extremely rapid manner by selectively applying voltage at the proper crystal inputs 21. The average switching time available with the inven tion is one milli-microsecond. This is a million times faster than present day mechanical switches.

Over a 200 me. bandwidth the switch has exhibited an insertion loss of less than 2.5 db and a rejection of greater than 30 db. The dielectric sleeve 38 which surrounds each of the crystals 2t) causes a bunching of the field in the center of the guide 12 where the crystal is located. As a result of this bunching of the field about the crystal, the switch rejection is greatly improved over the per formance of the switch without the sleeves 38.

A further improvement in performance can be achieved through use of two crystals 20 in each waveguide 12 instead of one. This situation is shown schematically in FIG. 4. The structure shown in FIG. 3 would be identical in every respect with the one exception that a second crystal would be placed in the waveguide 12 a quarter wavelength from the first crystal. In order to include a. second crystal in the guide the overall diameter of the switch must be increased slightly. The only disadvantage to the use of two crystals is that although the switch rejection will be doubled, the switch insertion loss will also be doubled.

It should be understood that reciprocity applies to all of the components in this embodiment of the invention so that the switch may be used to couple a single input to a plurality of outputs with little or no loss of efficiency.

A second embodiment of the invention is shown in FIGS. 5 and 6. The connectors and crystal mounts shown are essentially the same as those used in conjunction with the circular switch of FIG. 1 and so the structural details or these components will not be described in detail in conjunction with this embodiment. As can be seen from FIG. 5 the switch is basically Y-shaped having three equal waveguide arms 60, 61 and 62 separated from one another by an angle of Each of the arms 60, 61 and 62 contain an input connector as, an output connector 66 and a pair of RF choke crystal mounts 67 and 68 located on either side of the input connector 65 and carrying crystals 69 and 70, respectively. At the center of the switch where the waveguide arms form a small central cavity a second output connector '71 is positioned between the three crystal mounts 68. As in the previous embodiment all of the crystals are surrounded by dielectric sleeves to increase their efiiciency as reflectors of RF energy and all of the input and output probes are surrounded by dielectric sleeves to provide a standard 50 ohm input and output impedance.

All of the crystals in the switch provide a similar function. In contrast to the circular switch embodiment of FIG. 1 where the crystals provided a barrier to RF energy in the unbiased state, the crystals in the Y-shaped embodiment act as reflectors in a coax-to-waveguide adapter. That is, rather than serve as a barrier to energy flow they determine the direction of energy flow.

Energy introduced into input 65 in waveguide arm 61 will travel down waveguide 61 in both directions. However, if both of the crystals 69 and 7t) are unbiased they will provide a reflecting wall at the point at which they are located. It now crystal 69 is biased energy will travel past the crystal 69 to output 66. Energy traveling toward the center of the switch will be reflected without appreciable loss by crystal 7t which is located an odd multiple of a quarter Wavelength from input connector 65. On the other hand if crystal 7% is biased rather than crystal 69, crystal 7t) will pass the energy while crystal 69 located an odd multiple of a quarter wavelength from input 65 will provide a reflecting wall at this location. As can be seen the crystals 69 and 70 are used to match the coaxial inputs to the waveguides and thereby determine the direction of energy flow from the input 65.

The crystals 7% are also used to match the waveguide to the output coaxial connector 71. When a pair of the crystals 7% are unbiased they form at the proper distance a V-shaped reflecting Wall behind the output '71 so as to properly match the Waveguide to the coaxial connector. For example, if the crystals 70 in waveguides 6t? and 62 were unbiased and the crystal 70 in waveguide 61 were biased, energy from input 65 in wavegude 61 would be coupled to the output 71.

This second embodiment provides several combinations of high speed switching of RF energy. From the inputs 65 energy may be switched to the individual outputs 66 by biasing crystals 69 or this energy may be switched to the common output '71 by biasing crystals 70. Another possibility is the simultaneous switching of energy from input 65 to both outputs 66 and 71 by biasing both crystals 69 and 7t) in any given waveguide arm. In the latter case the power input would be divided between the two outputs 66 and 71.

The switch shown in FIGS. 5 and 6 has the same advantages of extremely fast switching time and high isolation as achieved with the embodiment of FIG. 1 and like the first embodiment all components are subject to reciprocal operation where such operation is desirable.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A waveguide switch comprising a plurality of waveguide arms, each arm having an end in contiguous relationship with an end on each of the other arms, an input wave coupler in each waveguide arm, an output Wave coupler common to each of said waveguide arms, a diode crystal located in each waveguide arm between each or" said input wave couplers and said output wave coupler to facilitate the switching of RF energy from each of said inputs to said output, and a dielectric sleeve surrounding said diode for increasing the isolation effect of said diode.

2. A waveguide switch comprising an upper mounting plate formed with an axially located hole, an upwardly directed flange attached to said upper plate and positioned to surround said hole, a lower mounting plate, a plurality of waveguide sections positioned between said plates, each of said sections being formed with an inner and an outer end, a cavity formed by the intersection of adjacent inner ends of said waveguide sections and located under said hole, a first RF wave coupler in each of said waveguide sections, a second RF wave coupler located in said cavity, a diode located in each waveguide section between said first wave coupler and said second wave coupler, a dielectric sleeve surrounding said diode for increasing the isolation effect of said diode, means for changing the impedance of said diodes so as to permit passage of RF energy through the waveguide sections, and a plug threadedly engaged with said flange and adapted to extend to various depths into said cavity, whereby the volume of said cavity is altered by said plug, thereby changing the resonant frequency of said cavity and the frequency at which the switch will operate.

3. A waveguide switch comprising an upper mounting plate formed with an axially located hole, an upwardly directed flange attached to said upper plate and positioned to surround said hole, a lower mounting plate, a plurality of waveguide sections positioned between said plates, each of said sections being formed with an inner and an outer end, a circular tuned cavity formed by the intersection of adjacent inner ends of each of said waveguide sections and located under said hole, a plug threadedly engaged with said flange and adapted to extend to various depths into said cavity, said plug additionally being formed with an axially located bore opening into said cavity, .a first wave coupler located at the outer ends of each of the waveguide sections, a second wave coupler extending through the center of said cavity and received by said bore, a diode located in each waveguide at the perimeter of said cavity, a dielectric sleeve surrounding said diode for increasing the isolation effect of said diode, and means for changing the impedance of said diodes so as to permit passage of RF energy between said cavity and said waveguide sections whereby the insertion of said second wave coupler into said bore provides a wide band response to said cavity.

4. A waveguide switch comprising an upper mounting plate formed with an axially located hole, an upwardly directed flange attached to said upper plate and positioned to surround said hole, a lower mounting plate, a plurality of waveguide sections positioned between said plates, each of said sections being formed with an inner and an outer end, a circular cavity formed by the intersection of adjacent inner ends of each of said waveguide sections and located under said hole, a plug threadedly engaged with said flange and adapted to extend to various depths into said cavity, said plug additionally being formed with an axially located bore opening into said cavity, an RF input probe located one quarter wavelength from the outer end of each waveguide section, an RF output probe extending through said cavity and secured by said bore, an RF choke crystal holder located in each waveguide at the periphery of said cavity and formed with an annular groove, a diode crystal in each said holder, a dielectric sleeve surrounding said diode for increasing the isolation effect of said diode, and control means for changing the impedance of said crystals so as to allow passage of RF energy between said waveguide sections and said cavity whereby said annular groove in said holder prevents the reflection of any RF energy from said crystal.

5. A waveguide switch comprising an upper mounting plate formed with an axially located hole, an upwardly directed flange attached to said upper plate and positioned to surround said hole, a lower mounting plate, a plurality of waveguide sections positioned between said plates, each of said sections being formed with an inner and an outer end, a circular cavity formed by the intersection of adjacent inner ends of each of said waveguide sections and located under said hole, a plug threadedly engaged with said flange thereby adapted to extend to various depths into said cavity, said plug additionally being formed with an axially located bore opening into said cavity, an RF input probe located near the outer end of each waveguide section, an RF output probe mounted on said lower mounting plate and extending through the center of said cavity, said output probe being partially received by said bore, an RF choke crystal holder located in each waveguide at the periphery of said cavity, a diode crystal in each said holder, a dielectric sleeve surrounding said diode for increasing the isolation eflect of said diode, and control means for changing the impedance of said crystals so as to allow passage of RF energy between said waveguide sections and said cavity, whereby said center cavity is tuned by rotatably moving said plug farther into said cavity for causing a larger portion of said probe to be inserted into said bore and thereby varying the electrical length of said output probe and in turn the resonant frequency of said cavity.

6. A microwave switch comprising first, second and third waveguide arms, a triangular cavity to which said waveguide arms are attached, an RF input probe located in the center of each waveguide arm, first RF output probes positioned at the outer ends of each waveguide arm, a second RF output probe positioned in the center of said triangular cavity, first crystal diodes positioned at the periphery of said triangular cavity in each waveguide arm, second crystal diodes positioned between each of said first output probes and said input probes at an at the periphery of said triangular cavity in each waveguide arm, second crystal diodes positioned between each transparent to RF energy so as to direct energy within each guide arm from the input probe to one of said output probes.

7. A microwave waveguide switch comprising first, second and third waveguide arms intersecting at an angle of a plurality of RF input and output connectors, each waveguide arm having an input connector at the center and an output connector at the outer end thereof, an output connector in the center of said intersecting region, a plurality of crystal diodes, a dielectric sleeve surrounding each of said diodes, each waveguide arm having a first crystal diode across the guide at the edge of said intersecting region and a second crystal diode across the guide between said input and output connectors, and means for altering the impedance of said crystal diodes so as to selectively direct RF energy in the waveguide arms to one of said output connectors.

References Cited by the Examiner UNITED STATES PATENTS 3,069,629 12/62 Wolif 333-7 (Other references on following page) FOREIGN PATENTS Techniques, v01. MTT-6, October 1958, pages 378 to 383. 718865 11/54 Great Bntam' Pound: Microwave Mixers, Radiation Laboratory OTHER REFERENCES Series, vol. 9, McGraw Hill C0,, 1948.

Garver et 211.: Microwave Semiconductor Switching 5 Techniques, IRE Transactions on Microwave Theory and HERMAN KARL SAALBACH, Examine"- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,l78 ,659 April 13, 1965 John V. Smith et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, lines 52 and 53, for "at the periphery of said triangular cavity in each waveguide arm, second crystal diodes positioned between each" read odd multiple of a quarter wavelength from said input probes, and means rfor selectively rendering said crystals Signed and sealed this 28th day of September 1965.

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,178 ,659 April 13, 1965 John V. Smith et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, lines 52 and 55, for "at the periphery of said triangular cavity in each waveguide arm, second crystal diodes V positioned between each'Vread odd multiple of a quarter wavelength from said input probes, and means for selectively rendering said crystals Signed and sealed this 28th day of September 1965.

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER- Attesting Officer Commissioner of Patents 

1. A WAVEGUIDE SWITCH COMPRISING A PLURALITY OF WAVEGUIDE ARMS, EACH ARM HAVING AN END IN CONTIGUOUS RELATIONSHIP WITH AN END ON EACH OF THE OTHER ARMS, AN INPUT WAVE COUPLER IN EACH WAVEGUIDE ARM, AN OUTPUT WAVE COUPLER COMMON TO EACH OF SAID WAVEGUIDE ARMS, A DIODE CRYSTAL LOCATED IN EACH WAVEGUIDE ARM BETWEEN EACH OF SAID INPUT WAVE COUPLERS AND SAID OUTPUT WAVE COUPLER TO FACILITATE THE SWITCHING OF FOR ENERGY FROM EACH OF SAID INPUTS TO SAID OUTPUT, AND A DIELECTRIC SLEEVE SURROUNDING SAID DIODE FOR INCREASING THE ISOLATION EFFECT OF SAID DIODE. 